Elixir:
Reading command line arguments

How to:

In Elixir, grabbing command line arguments is a no-brainer. Use System.argv() and you’ll snag them as a list of strings.

defmodule CliArgs do
  def main do
    args = System.argv()
    IO.inspect(args)
  end
end

CliArgs.main()

Run this being like elixir cli_args.exs foo bar baz, and expect:

["foo", "bar", "baz"]

You’re seeing the arguments foo, bar, and baz right there in an Elixir list.

Deep Dive

Historically, command line arguments are as old as the hills, stemming from early CLI environments. In Elixir, System.argv() is your trusty steed for this job. Why? Because it’s baked into the Erlang VM, which Elixir is built on top of.

Alternatives? Sure, you’ve got libraries that parse arguments for you, adding flags and options. But for vanilla Elixir, System.argv() is the way to go.

Implementation wise, it’s important to remember that System.argv() gives you all arguments as strings. If you need numbers or other types, you’ll have to convert them manually. Also, the order matters. Your first command line argument is List.first(System.argv()), and so on.

See Also

For more, check out:

• Elixir’s System module docs for other handy system-related functions.
• Optparse in Elixir’s standard library, which is a beast for parsing command line options.
• Erlang’s init docs if you’re curious about the under-the-hood VM magic that supports Elixir.